Piston construction for compressor units



Nov.

vQcRoNsTED-r ET A1. PTSTON CONSTRUCTION FOR COMPRESSOR UNITS Filed July 25, 1 943 3 Sheets-Sheet 1 FIG.

d A- TORNEY Nov. 5, 194s.

-v cRoNsTEDT v|51- AL Filed July 23, 1943 O PIS'TON CONSTRUCTION FOR COMPRESSOR UNITS 5 Sheets-Sheet 2 ATTORNY FIG. 2

Nov. 5, 1946. v.- cRoNsTEDT ETAL I 21,410,428

I I PISTON CONSTRUCTION FOR COMPRESSOR UNITS i 3 Sheets-*Sheet 5 Filed July y2s, 194s Y//////////// ,//f/I Patented Nov. 5, 1946 PISTON CONSTRUCTION FOR COMPRESSOR UNITS Val Cronste'dt, Marlboro, and Andrew Kalitnsky, Eagleville, Conn., assignors to United Aircraft Corporation. East Hartford, Conn., a corporation of Delaware Application July 23, 1943, serial No. 495,933 f 9 Claims.

Large diameter pistons, particularly in highspeed machines such as the compressor pistons of engine-and-compressor units, are subjected to bending stresses resulting from the high acceleration of the piston at opposite ends of its stroke. An object of this invention is to reinforce the piston against shear resulting from these bending stresses.

The compressor piston must be thick enough to carry sealing rings at it-s periphery and must have substantially flat side walls for minimizing the clearance volume at the ends of its stroke.. Such a piston, if solid, is relatively heavy and requires the rest of the machine to be heavy in order to operate successfully. A feature of this invention is a piston which is made hollow to reduce weight and which is still strong enough to withstand the shear resulting from the bending stresses on the piston.

The rate of reciprocation of the pistons in a free-piston engine-and-compressor unit is dependent upon the weights of the moving part-s. Lightening the piston to increase its rate of reciprocation may reduce the strength of the piston, particularly the large diameter compressor piston so that it is no longer strong enough to withstand the forces acting on it. A feature of this invention is'a reinforced piston which is light in weight.

Other objects and advantages will be apparent from the specication and claims and from the accompanying drawings which illustrate an embodiment of the invention.

Fig. 1 is a longitudinal sectional View through a free-piston unit showing the pistons therein.

Fig. 2 is a sectional view through one of the piston assemblies, showing o-ne side disc of the compressor piston in elevation.

Fig. 3 i-s an enlarged longitudinal section of a part of the piston.

Fig. 4 is a sectional View through the intake valve.

The unit shown includes an engine cylinder l having reciprocating pistons I2 and I4 to which compressor pistons I6 and I8 in cylinders 2D and 22 are integrally connected. Sleeves 24 and 26 attached to the compressor pistons complete the reciprocating piston assemblies; The sleeves in combination with stationary pistons 28 and 30 form air spring cylinders.

The piston assemblies are moved apart by the burning of fuel injected into engine cylinder l0. Air compressed in the air spring cylinders on the power stroke returns the piston assemblies.. The assemblies are always maintained at equal distances from the center of the engine cylinder by a linkage, which may include racks 34 extending from the compressor pistons and engaging a pinion 36.

Intake manifold 38 conducts air to intake valves 46, see Fig. 4, through which air alternately enters opposite end-s of the compressor cylinders. The compressed air leaves the cylinders through discharge valves 42, similar to valves 4i), and also at opposite ends of the compressor cylinders, and passesv through scavenge manifold 44 through ports 46 and 48 which are uncovered by pistons l2 and i4 at the end of the power stroke, thereby permitting air to be blown through the engine cylinder and exhaust ports 50 and 52 into exhaust manifold 54. Valves 40 and 42 may be the type shown, for example, in Huil Patent Number 1,599,414, dated September 14, 1926.

Each compressor piston I6 and i8 is made up of opposed discs 56 and 58, the former being integral with a hub 66 on which the engine piston 44 and air spring or sleeve 26 may be mounted. Disc 56, forming the inner surface of the compressor piston is clamped against disc 56 by the engine piston and is also held in place by bolts 62 extending through opposed bosses 64 and 66 on discs 56 and 58 which hold the discs in spaced relation. Both discs have opposed radially extending ribs 68 and lll engaging each other. The contacting surfaces of bosses 64 and 66 and ribs 66 and lll are provided with serrations 'l2 to prevent any relative movement between the discs. These serrations or grooves are at right angles to the radius of the disc as shown and thus resist shear stresses in the discs.

Either or both discs may also have circumferentially extending ribs 14 and other radially eX- tending ribs F6 which are not thick enough to engage with the opposite disc but which act as reinforcement for the disc on which they are formed. The ribs may extend between adjacent bosses 64 on disc 56 or bosses 66 on di-sc 58. These bosses act as spacers for the opposed discs 56 and 58 and prevent buckling of the discs when bolts 62 are tightened.

It is to be under-stood that the invention is not limited to the specic embodiment herein illustrated and described, but may be used in other ways without departure from its spirit as dened by the following claims.

We claim:

1. A piston including opposed discs having ribs on the adjacent surfaces engaging each other and serrations on the adjoining rib surfaces. v

2. A piston including opposed discs having ribs adjacent surfaces and fastening meansfengaging said bosses to hold the discs together.

6. A piston including opposed discs having a number of interengaging serrate bosses on the adjacent surfaces, and bolts extending through said bosses to hold the discs together.

'7. A piston including opposed discs having a number of similarly arranged ribs on Vthe adjacent surfaces, said ribs having interengaging teeth and grooves to prevent relative movement between the ribs.

8. A piston including opposed discs having similarly arranged radial ribs on the adjacent surfaces, said ribs having interengaging teeth and grooves extending transversely of the ribs to prevent relative movement radially between the discs.

9. A piston including opposed discs having similarly arranged radial ribs on the adjacent surfaces, said ribs having interengaging teeth and grooves extending transversely of th'e ribs to prevent relative movement radially between the discs, and means for fastening the discs together with the teeth and grooves in engagement.

VAL CRONSTEDT. ANDREW KALITINSKY. 

